Method of preparing washed photographic emulsions



United States Patent METHOD OF PREPARING WASHED PHOTO- GRAPHIC EMULSIONSFrederick J. Russell, Rochester, N. Y., assignor to Eastman KodakCompany, Rochester, N. Y., a corporation of New Jersey ApplicationJanuary 25, 1954,

Serial'No. 406,061

7 Claims. (Cl. 95-7) No Drawing.

: following compounds The preparation of the dispersed silver halide ingelatin 9 by mixing a water solution of the silver salt (such as silvernitrate) with a water solution of a water-soluble halide (such as sodiumchloride). The gelatin may be dissolved in either or both of thesolutions or in a separate solution. After the silver halide is formedthe dispersion thereof may be digested or treated in some other mannerto impart the desired characteristics. To refine the silver halidedispersion it is first chilled and allowed to set or gel. The gel thusformed is noodled or otherwise comminuted and the water soluble saltspresent therein are dialyzed out with water having a low temperature.After the salts have been removed and the water is drawn off, the washedemulsion may then be melted by warming and gelatin or some otherchemicals may be added to condition the silver halide grains thusobtained.

I have found a process for preparing silver halide emulsions in whichthe chilling and setting steps are eliminated and the time required forsubsequent steps is considerably lessened. 7

One object of my invention is to provide a method for preparing washedsilver halide emulsions in which the silver halide may be coagulatedwithout the necessity of altering the pH thereof. Another object of myinvention is to provide a method for washing fine grained emulsions inwhich the tendency to form grain clumps is diminished. Another object ofmy invention is to provide a method for preparing washed silver halideemulsions in which change of the pH of the mass is not necessary toobtain coagulation of the emulsion. A further object of my invention isto provide a method of purifying a gelatin emulsion in which the saltsof certain metals have been found to be quite useful.

The prior art has suggested the washing of emulsions by coagulating thesame, and for this purpose there had been used as agents, salts of analkali metal or a metal of group II. Methods of coagulating have alsobeen described in which gelatin derivatives have been employed as thecarrier for the silver halide. In both of those cases, however, the pHof the silver halide dispersion was lowered to 4 or less to obtaincoagulation. In the case of emulsions characterized by fine grain thesettling of the coagulated material often occurs slowly and suchemulsions exhibit a tendency to form grain clumps which are difficult toredisperse after the washing has occurred.

I have now found that it is possible to coagulate emulsions in which thesilver halide is dispersed in certain gelatin derivatives, by theaddition to those silver halide dis persions of relatively small amountsof water soluble salts of-certain metals. The coagulation thus obtainedoccurs 2,768,079 i atenied Oct. 23, 1956 over'a considerable range in pHand the step of lowering the pH which has been necessary in manyprevious processes can be omitted. I have found that this method ofcoagulation washing of dispersed silver halide is particularlyadvantageous in the case of fine grained emulsions as rapid settling isobtained and the tendency to clump is reduced to a minimum.

The gelatin derivatives which I have found to be useful as peptizers fordispersing silver halide for preparing washed emulsions in accordancewith my invention are the aromatic sulfonyl chloride derivatives ofgelatin, the

derivatives of gelatin, the carcarboxylic acid chloride boxylicanhydride derivatives of gelatin, the aromatic isocyanate derivatives ofgelatin and the l,4-diketone derivatives of gelatin. The preparation ofthese gelatin derivatives is known in the prior art as disclosed, forexample, in U. S. Patent No. 2,614,929 of Yutzy and Russell, October 21,1952. As an example of gelatin derivatives which are useful forpreparing washed emulsions in accordance with my invention, the reactionproducts of any of the with. gelatin may be employed for that purpose.

Sulfonyl chlorides Carboxylic acid chlorides Phthalyl .chloridep-Nitrobenzoyl chloride Benzoyl chloride Ethyl chlorocarbonate Furoylchloride Acid anhydrides Phthalic anhydride Benzoic anhydride Succinicanhydride Maleic anhydride Is-atoic anhydride n-Heptyl succinicanhydride Hexahydrop'hthalic anhydride Isocyanates Phenyl isocyanatep-Bromophenyl isocyanate p-Chlorophenyl isocyanate p-Tolyl isocyanatep-Nitrophenyl isocyanate Alpha-naphthyl isocyanate fl-Naphthylisocyanate The preparing of a washed emulsion in accordance with myinvention is carried out by forming silver halide in an aqueous solutionof the gelatin derivative followed by adding to the so obtaineddispersion of silver halide a small amount of an aqueous solution of ametal salt of the type specified herein as being suitable. The metalsalt is employed in a proportion within the range of l/ 2 gram to 20grams per mol of silver halide, the amount needed depending upon theconditions residing in the emulsion.

It. appears that a greater concentration of the salt is desirablewithanincrease in pH anda lowertemperature. The salts which I have foundto beuseful for coagulating dispersions of silver halide in gelatinderivatives are the watersoluble salts of cadmium; zinc, aluminum, iron,

nickel; chromium; and lanthanum. The acoag'u'lationv has been found tooccur at any pH below 10, henceno adjust ment'of the pH is ordinarilynecessary. The amount. of v the metal salt which gives maximumcoagulation will vary depending upon; the particular salt. employed, thetemperature of the dispersion and the pH of the emulsion at the time ofcoagulation. For instance, in thecase of a dispersion-of silver halidein a gelatin derivative having a temperature of 30 C. and a pH ofthe-amount of cadmiumchloride which will give optimum result's'has been:foundto. be approximately 15.5 grams per mol of silver .halide. If thepH tends toward the acid side the amountvof salt neededto obtain optimumcoagulation becomes less as is also the case where the temperature ishigher. tin derivative having a pH of 4.8 and a temperature of 60 C. Ihave found that the optimum amount of lanthanum nitrate when employed asthe coagulating salt is. 1.3-2gms. In the use of cadmium chloride in adispersionhaving a pH of 4.8 at a temperature of optimum results areobtained when 3.45 grams of the cadmium chloride per mole of silverhalide is used. If the temperature is increased to C. the amountof'cadmium chloride necessary for optimum results in 2.3 grams while.

if the temperature is increased to 50 C., .57 grams of cadmium chlorideper mol of silver halide give optimum results. If the temperature of thedispersion is at 30 C. but the pH is at 6, 13.7 grams of cadmiumchloride per mol of silver halide is desirable, While if the pH is at8-10,

15.5 grams of cadmium chloride is desirable per mol of silver halide.-If, however, the temperature of the dispersion is at 50 C., the amountof cadmium chloride to obtain optimum results is 8.5 grams per mol ofsilver halide. Likevariations occur in the case of the other saltsspecified to obtain optimum coagulation conditions- As was pointed outabove the use of lanthanum nitrate in a silver halide dispersion havinga pH of 4.8 and a temperature of 60, 1.32 gms. thereof is the optimumfor coagulation. If, however, the temperature is dropped to 30 C. then1.76 gins. of lanthanum nitrate is the most desirable amount per mol ofsilver halide to obtain coagulation.

After the dispersion of silver halide in the gelatin derivative has beencoagulated the liquid portion thereof is removed from the settledportion such as by decantation. The silver halide may then beredispersed by adding water to the particle mass, preferably with theuse of a slightly elevated temperature and if desired, a washingwithwater having a temperature of 10 C. may be employed prior toredispersion. If desired, the dispersion may be recoagulated by againadding salt and decanting off the mother liquor. Upon redispersion it isdesirable to 'addthereto a solution of a carrier for the silver halidesuch as gelatin or far-hydrolyzed cellulose acetate to form aphotographic emulsion of the desired silver halide concentration.

The following examples illustrate my invention:

Example 1 potassium chloride and 2.6 grams of potassium iodide in 3000cc. of distilled water at 60 C. This wasaccomplished by-adding thesilvernitrate solution to the second.

solution over a period of approximately 10 minutes and maintainingthemixture at a temperature of;60 C. After the silver nitrate was addedtheernulsion was. cooled to 40 C. and 24 grams of cadmium chloride in.solution:in:

250 cc. of distilled water was added-thereto,;th'e-pH of the systembeing.6 .3 and a coagulum of gelatin derivative and silver halideformed. This coagulum was allowedato set -1 In the case of a silverhalide dispersion in a gelatle and the mother liquor was decantedtherefrom. 6 liters was dispersed for 5 minutes at 40 C. and there wasadded to this dispersion a solution of 10 grams of cadmium chloride in 100 cc. of distilled water at a pH of 6.3. The emulsion was againcoagulated and upon settling the supernatant liquor was decanted. Therewas then added 540 grams of photographic gelatin and additionaldistilled water to result in a total weight of the mass of 14 lbs. Theemulsion was held while agitating for 20 minutes at 40 C. at a pH of6.0. The so obtained emulsion was coated onto a cellulose acteate filmbase and upon exposing in an Eastman Ib sensitometer for A of a minuteand developed for 4 minutes inDeveloper D-19 at 68 F. the followingcharacteristics were found:

lO/i Speed21.5; Gamma 2.60; Fog 0.05 Example 2 A dispersion of silverhalide was preparedby mixinga solution of 400 grams of silver nitrate in3600 cc. .of distilled water at 30 C. with a solution of 59 grams ofbenzene sulfonyl chloride gelatin derivative, 142 grams of potassiumchloride and 57 grams of potassium bromide dissolved in 3400 cc. ofdistilled water at 30 C. The silver nitrate solution was added to thealkali halide gelatin solution over a period of approximately 2 minutes.with good stirring. The dispersion thus formed was heated to 40 C. andthe mass was found to have a pH of 5.95.

There was then added thereto an aqueous solution of 14.2. grams of'cadium chloride. The silver halide and gelatin derivative coagulatedand settled. After several minutes the mother liquor was decanted Off.The coagulum. was rinsed in cold tap water and 8 liters of distilledwater was added to thecoagulum and the mass was stirred at 40 C. untildispersion occurred. An aqueous solutionof 800 grams of photographicgelatin was added and sufficient distilled water was then added to bringthe total weight of the mass to 20 lbs. The emulsion was stirred at 40C'. to obtain-completedispersion and the pH was adjusted to 6.5 by theaddition of the required amount of the aqueous sodium hydroxide. Themass was digested- Example 3 A dispersion of silver halide in gelatinderivative was prepared by mixing a solution of 400 grams of 'silvernitrate in 4100 cc. of distilled water at 72 C. with a solution 'of 59grams of n-heptyl succinic anhydride gela- 1 tin derivative, 330 gramsof potassium bromide and 6 grams of potassium iodide in 3400 cc. ofdistilled water at 70 C. The silver nitrate solution was added to thesecond solution over a period of approximately 5 /2 minutes with goodstirring, the temperature having beenmaintained at 70 C. The dispersionwas then stirred for 20 minutes at 70 C. and cooled at 40 C. 27 grams ofcadmiumchloridein aqueous solution were added ata pH of 6.0 whichcoagulated the emulsion and the coagulum was allowed to settle for a fewminutes. The residual liquid was decanted off and the coagulum wasrinsed in cold tap water. The particle mass thus obtained was mixed with16 lbs. of distilled water and the mass was stirred for 5 minutes at 40C. 590 grams of photographic gelatin was added and the mass was stirredfor 20 1ninutes-at40 C. until complete dispersion had been effected.Distilled water was then .added to bring the veloped for 4 minutes inD-19 developer at 68 F., it was found to have the followingcharacteristics:

30/E Speed 40; Gamma 1.97; Fog 0.04 Example 4 A dispersion of silverhalide was prepared in substantially the same manner as described inExample 3 but 59 grams of a hexahydrophthalic anhydride derivative ofgelatin was employed instead of the n-heptyl succinic anhydride gelatinderivative. The coagulation was induced by the use of lanthanum nitraterather than cadmium chloride. The emulsion finally obtained was coatedonto a cellulose acetate film support and Was exposed and developed asin the preceding example. The emulsion was found to have the followingcharacteristics:

30/E Speed 102; Gamma 2.80; Fog 0.06

The salts which may be employed for coagulating silver halidedispersions in accordance with my invention may be any of the watersoluble salts of the metal referred to. This would include the nitratesor chlorides of all of the metals listed although in many cases othersalts would be useful providing the negative ion of the salt does nothave any adverse eifect photographically or otherwise on the silverhalide dispersion.

I claim:

1. In a process of preparing a washed silver halide dispersion the stepswhich comprise preparing a dispersion of silver halide in an aqueoussolution of a gelatin derivative selected from the group consisting ofthe aromatic sulfonyl chloride derivatives of gelatin, the carboxylicacid chloride derivatives of gelatin, the carboxylic acid anhydridederivatives of gelatin and the aromatic isocyanate derivatives ofgelatin, coagulating that dispersion while at a pH of 4.5- by addingthereto 1/2-20 grams, per mole of silver halide, of a water soluble saltselected from the water soluble salts of cadmium, zinc, aluminum, iron,nickel, chromium and lanthanum whereby silver halide-gelatin granulesform and separating those granules from the liquid portion of the mass.

2. In a method of preparing a washed silver halide dispersion the stepswhich comprise forming a dispersion of silver halide in an aqueoussolution of a benzene sulfonyl chloride gelatin derivative, coagulaingthat dispersion while at a pH of 4.5l0 by adding thereto an aqueoussolution of 1/2-20 grams per mole of silver halide of a salt selectedfrom the water soluble salts of cadmium, zinc, aluminum, iron, nickel,chromium and lanthanum whereby silver halide-gelatin granules are formedand separating the thus formed granules from the liquid portion of themass.

3. In a method of preparing washed silver halide dispersions the stepwhich comprises forming a dispersion of silver halide in an aqueoussolution of hexa hydro phthalic anhydride-gelatin derivative,coagulating that dispersion while at a pH of 4.5-10 with 1/2-20 grams oflanthanum nitrate per mole of silver halide whereby silverhalide-gelatin granules are formed and separating those granules fromthe liquid portion of the mass.

4. In a method of preparing washed silver halide dispersions the stepswhich comprise forming a dispersion of silver halide in an aqueoussolution of a N-heptyl succinyl anhydride derivative of gelatin,coagulating that dispersion while at a pH of 4.5-10 by adding thereto anaqueous solution of 1/2-20 grams of cadmium chloride per mole of silverhalide whereby silver halide-gelatin granules are formed and separatingthose granules from the liquid portion of the mass.

5. In a method of preparing washed silver halide dispersions the stepswhich comprise forming a dispersion of silver halide in an aqueoussolution of a benzene sulfonyl chloride derivative of gelatin,coagulating the silver halide dispersion while at a pH greater than 4.5and not more than 10 by adding thereto an aqueous solution of 1/2-20grams of cadmium chloride per mole of silver halide whereby silverhalide-gelatin granules are formed and separating those granules fromthe liquid portion of the mass.

6. In a method of preparing a washed silver halide dispersion the stepswhich comprise forming a dispersion of a silver halide in an aqueoussolution of a gelatin derivative selected from the group consisting ofthe aromatic sulfonyl chloride derivatives of gelatin, the carboxylicacid chloride derivatives of gelatin, the carboxylic acid anhydridederivatives of gelatin and the aromatic isocyanate derivatives ofgelatin, coagulating the silver halide dispersion while at a pH of4.5-10 by adding thereto an aqueous solution of 1/2-20 grams of cadimumchloride per mole of silver halide whereby silver halide-gelatingranules are formed and separating those granules from the liquidportion of the mass.

7. In a process of preparing a washed silver halide dispersion the stepswhich comprise preparing a dispersion of silver halide in a gelatinderivative selected from the group consisting of the aromatic sulfonylchloride derivatives of gelatin, the carboxylic acid chloridederivatives of gelatin, the carboxylic acid anhydride derivatives ofgelatin and the aromatic isocyanate derivatives of gelatin, having a pHof 4.5-10 coagulating that dispersion without adjustment of the pHthereof by adding thereto 1/ 2-20 grams per mole of silver halide of awater soluble cadmium salt whereby silver halide-gelatin granules formand separating those granules from the liquid portion of the mass.

References Cited in the file of this patent UNITED STATES PATENTS2,614,928 Yutzy et al. Oct. 21, 1952 2,614,929 Yutzy et al. Oct. 21,1952 2,618,556 Hewitson et al Nov. 18, 1952

1. IN A PROCESS OF PREPARING A WASHED WILVER HALIDE DISPERSION THE STEPSWHICH COMPRISE PREPARING A DISPERSION OF SILVER HALIDE IN AN AQUEOUSSOLUTION OF A GELATIN DERIVATIVE SELECTED FROM THE GROUP CONSISTING OFTHE AROMATIC SULFONYL CHLORIDE DERIVATIVES OF GELATIN, THE CARBOXYLICACID CHLORIDE DERIVATIVES OF GELATIN, THE CARBOXYLIC ACID ANHYDRIDEDERIVATIVES OF GELATIN AND THE AROMATIC ISOCYANATE DERIVATIVES OFGELATIN, COAGULATING THAT DISPERSION WHILE AT A PH OF 4.5-10 BY ADDINGTHERETO 1/2-20 GRAMS, PER MOLE OF SILVER HALIDE, OF A WATER SOLUBLE SALTSELECTED FROM THE WATER SOLUBLE SALTS OF CADMIUM, ZINC, ALUMINUN, IRON,NICKEL, CHROMIUM AND LANTHANUM WHEREBY SILVER HALIDE-GELATIN GRANULESFORM AND SEPARATING THOSE GRANULES FROM THE LIQUID PORTION OF THE MASS.